THE signal being emitted has the same frequency as a plane's black box device.

A CHINESE ship has detected a second so-called pulse signal while searching for missing flight MH370 in the Indian Ocean.

The patrol ship Haixun 01 has twice picked up a "ping" with a frequency of 37.5kHz - the same frequency as a plane's black box.

International search planes and ships are now heading to the area.

It was earlier revealed that a Chinese air force plane had spotted several white floating objects in the ocean.

Retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the search operation, told reporters in Perth that two reported acoustic detections from Haixun 01 were a good lead.

However, he stressed there remained no certainty that the "pings" had come from the missing plane.

Houston said the first detection by Haixun 01 yesterday was followed by a second detection less than two kilometres away from the original "acoustic event".

The acoustic detections, he said, were separated by a period of 24 hours and the second detection lasted for around 90 seconds.

The water is 4.5 kilometres deep in the area where the where signals were picked up, making the search "incredibly challenging," Houston added.

Up to 10 military planes, two civilian jets and 13 ships are scouring a 88,000-sq-mile patch of desolate ocean northwest of Perth near where investigators believe the plane went down on March 8 with the loss of all 239 crew and passengers on board.